Chapter 3: Displaying &
Describing Categorical Data
Ways to present categorical data
 You’ve seen data represented in newspapers,
magazines, online
 How do you normally see it?
Ways to present categorical data
 You’ve seen data represented in newspapers,
magazines, online
 How do you normally see it?
 Tables (frequency tables)
 Bar charts
 Pie charts
 Line graphs
 Contingency tables
BGE outages as of 8/30/2011 8:27pm
County
Total
Customers
Customers
Out
Customers
Restored
Anne Arundel
236,540
47,236
134,639
Baltimore
369,037
69,381
170,091
Baltimore City
278,092
26,073
93,697
Calvert
8,003
2,475
5,581
Carroll
57,564
6,698
17,406
Harford
100,987
14,274
74,295
Howard
120,951
9,631
35,501
Montgomery
13,635
2,316
10,257
Prince George's
81,791
8,021
23,479
Total:
1,266,600
186,105
564,946
Source: bge.com
Bar Chart of Customers Restored
180,000
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
Anne Arundel
Baltimore
Baltimore City
Calvert
Carroll
Harford
Howard
Montgomery
Prince George's
Pie Chart of Customers Restored
Anne Arundel
Baltimore
Baltimore City
Calvert
Carroll
Harford
Howard
Montgomery
Prince George's
Contingency Tables
 Look at 2 categorical variables together and see if
there is a relationship between them
 Data from passengers on Titanic
Source: Intro Stats, DeVeaux
Contingency Table as Percentages
Source: Intro Stats, DeVeaux
Conditional Distributions
 Show the distribution of one variable based on a
specific condition of the other
 Conditional distribution of ticket class conditioned
on each value of survival
Source: Intro Stats, DeVeaux
Conditional Distributions
 Conditional distribution of survival conditioned on
each value of ticket class
Source: Intro Stats, DeVeaux
Side-by-Side Bar Chart of conditional distribution of
survival for each category of ticket class
Source: Intro Stats, DeVeaux
Improper Graphs
Source: Intro Stats, DeVeaux
Improper Graphs
Source: Intro Stats, DeVeaux
Improper Graphs
Source: Intro Stats, DeVeaux